The present invention relates to new liquid crystalline compounds and liquid crystal compositions. More particularly, the present invention relates to terphenyl derivatives having a fluorine-substituted-1,4-phenylene group, liquid crystal compositions containing them, and liquid crystal display devices made using the liquid crystal compositions.
Liquid crystal display devices using liquid crystalline compounds (in this description, the term xe2x80x9cliquid crystalline compoundxe2x80x9d is used as a generic term for a compound exhibiting a liquid crystal phase or a compound not exhibiting a liquid crystal phase but useful as a constituent of a liquid crystal composition) are widely used in displays of clocks, watches, electronic calculators, word processors and the like. Lately, much research has been conducted for a TFT type display having characteristics such as a high contrast and a broad visual field angle.
Liquid crystal compositions for TFT need physical properties, such as a high voltage holding ratio, low threshold voltage (Vth), little variation of these properties with temperature, broad temperature range of liquid crystal layers, excellent compatibility with other liquid crystal materials and low viscosity. Further, the compositions having a high optical anisotropy (xcex94n) are useful for improving the response speed.
For these reasons, as a component of liquid crystalline compounds having such characteristics, fluorine-substituted liquid crystalline compounds are preferably used, as described in (1) Japanese Patent Publication 63-13411, (2) Japanese Patent Publication 63-44132, (3) Japanese Patent Laid-open 2-233626, (4) Japanese Patent Laid-open 2-501311, (5) Japanese Patent Laid-open 3-500413, (6) Japanese Patent Laid-open 3-504018, (7) Japanese Patent Laid-open 5-502676, (8) Japanese Patent Laid-open 6-504032, (9) GB2257701 and (10) EP439089, many synthesis methods and researches have been done.
It is an object of the present invention to provide liquid crystalline compounds having a very little variation of these properties with temperature change, high xcex94n, and good compatibility with other liquid crystal materials particularly at low temperatures, liquid crystal compositions containing these compounds, and liquid crystal display devices made using the liquid crystal compositions.
The present inventors have earnestly studied to resolve the above problems and have completed the studies by obtaining the merphenyl derivatives having the above properties. The compounds are represented by general formula (1); 
wherein R represents a straight or branched alkyl group of 1-20 carbon atoms, and any methylene groups (xe2x80x94CH2xe2x80x94) not adjacent each other in each alkyl group may be replaced by oxygen atoms; X shows an halogen atom, xe2x80x94OCF3, xe2x80x94OCF2H, xe2x80x94CF3, xe2x80x94CF2H or xe2x80x94CFH2; Y1, Y2, Y3, Y4, Y5 and Y6 independently represents H or F, but at least two of Y1, Y2, Y3 and Y4 represent F;
in which
a) in case of Y1xe2x95x90Y2xe2x95x90Y3xe2x95x90Y4xe2x95x90H and Xxe2x95x90F, Y5xe2x95x90Y6xe2x95x90F,
b) in case of Y1xe2x95x90Y2xe2x95x90F, Y3xe2x95x90Y4xe2x95x90H and Xxe2x95x90xe2x80x94CF3 or xe2x80x94CF2H, Y5xe2x95x90Y6xe2x95x90F or Y5xe2x95x90Y6xe2x95x90H,
c) in case of Y1xe2x95x90Y3xe2x95x90F, Y2xe2x95x90Y4xe2x95x90H and Xxe2x95x90xe2x80x94CF3, Y5xe2x95x90Y6xe2x95x90F,
d) in case of Y1xe2x95x90Y3xe2x95x90F, Y2xe2x95x90Y4xe2x95x90H and Xxe2x95x90xe2x80x94OCF3, Y5xe2x95x90F,
e) in case of Y3xe2x95x90Y4xe2x95x90F, Y1xe2x95x90Y2xe2x95x90H and Xxe2x95x90F, Y5xe2x95x90Y6xe2x95x90F,
f) in case of Y3xe2x95x90Y4xe2x95x90F, Y1xe2x95x90Y2xe2x95x90H and Xxe2x95x90xe2x80x94OCF3 or xe2x80x94CF3, Y5xe2x95x90F,
g) in case of Y1xe2x95x90Y2xe2x95x90Y3xe2x95x90F, Y4xe2x95x90H and Xxe2x95x90CL, Y5xe2x95x90Y6xe2x95x90F,
h) in case of Y1xe2x95x90Y2xe2x95x90Y3xe2x95x90F, Y4xe2x95x90H and Xxe2x95x90F, xe2x80x94CF3 or xe2x80x94CF2H, Y5xe2x95x90F, and
i) in case of Y1xe2x95x90Y2xe2x95x90Y3xe2x95x90Y4xe2x95x90F and Xxe2x95x90Cl or xe2x80x94OCF3, Y5xe2x95x90F,
however, in case of Y1xe2x95x90Y2xe2x95x90F and Y3xe2x95x90Y4xe2x95x90H, in case of Y1xe2x95x90Y3xe2x95x90F and Y2xe2x95x90Y4xe2x95x90H, and in case of Y3xe2x95x90Y4xe2x95x90F and Y1xe2x95x90Y2xe2x95x90H, not Xxe2x95x90Cl,
and any atom in the compound may be replaced by an isotope thereof.
A part of the compounds represented by general formula (1) are formally included in the compounds described in the above references (6) to (10). However, in these references, there is no description of data such as values of physical properties of the compounds of the present invention, and definite or embodied characteristics of these compounds, so that the present invention is not suggested.
The compounds represented by general formula (1) and be classified as follows into (a-1) to (a-6).
Rxe2x80x94B(F,F)xe2x80x94Bxe2x80x94Qxe2x80x83xe2x80x83(a-1)
Rxe2x80x94Bxe2x80x94(F)xe2x80x94B(F)xe2x80x94Qxe2x80x83xe2x80x83(a-2)
Rxe2x80x94Bxe2x80x94B(F,F)xe2x80x94Qxe2x80x83xe2x80x83(a-3)
Rxe2x80x94B(F,F)xe2x80x94B(F)xe2x80x94Qxe2x80x83xe2x80x83(a-4)
Rxe2x80x94B(F)xe2x80x94B(F,F)xe2x80x94Qxe2x80x83xe2x80x83(a-5)
Rxe2x80x94B(F,F)xe2x80x94B(F,F)xe2x80x94Qxe2x80x83xe2x80x83(a-6)
In the formula, R represents as the same meaning as described above, B represents a 1,4-phenylene group, B(F) represents a 3-fluoro-1,4-phenylene, B(F,F) represents a 3,5-difluoro-1,4-phenylene group, and Q represents the following group: 
wherein Y5, Y6 and F represent as the same meaning as described above.
As described above, in the formula, R represents a straight or branched alkyl group of 1-20 carbon atoms. As a straight alkyl group, methyl, ethyl, propyl, butyl, pentyl, hexyl, heptyl, decyl, pentadecyl or eicosyl can be exemplified. As a branched alky group, isopropyl, secbutyl, tert-butyl, 2-methyl-butyl, isopentyl, isohexyl, 3-ethyloctyl, 3,8-dimethyltetradecyl or 5-ethyl-5-methylnonadecyl can be exemplified. Further, the branched alkyl group may be optionally active group, and compounds having such a group are useful as chiral doping agents.
Any methylene groups not adjacent each other in the alkyl groups may be replaced by oxygen atoms, and alkoxy groups such as methoxy, ethoxy, propoxy, butoxy, pentyloxy and nonyloxy, and alkoxyalkyl groups such as methoxymethyl, methoxyethyl, methoxypropyl, methoxybutyl, methoxypentyl, methoxyoctyl, ethoxymethyl, ethoxyethyl, ethoxypropyl, ethoxyhexyl, propoxymethyl, propoxyethyl, propoxypropyl, propoxypentyl, butoxymethyl, butoxyethyl, butoxybutyl, pentyloxymethyl, pentyloxybutyl, hexyloxymethyl, hexyloxyethyl, hexyloxypropyl, heptyloxymethyl and octyloxymethyl are examples thereof.
Although the liquid crystalline compounds of the present invention represented by general formula (1) may be prepared by a method of common organic synthesis, as an example, the compounds may be easily prepared by the following method. 
wherein R, Y1-Y6 and X have the same meaning as described above, Xa and Xb are halogen atoms.
Namely, as shown in scheme 1, in mixed solvent of three ingredients; toluene, xylene or the like, alcohol such as ethanol, and water; halogen compound (2) and dihydroxyborane derivative (3) can be reacted in the presence of a base such as K2CO3 or Na2CO3 and a catalyst such as carbon-carried palladium (Pdxe2x80x94C), Pd(PPh3)4 or PdCl2(PPh3)2 to produce compound (1) of the present invention. Further, as shown in scheme 2, after reacting halogen compound (2) with a lithium compound such as n-BuLi or sec-BuLi and a zinc compound such as ZnCl2 or ZnBr2, the reactant may be reached with halogen compound (4) to obtain the above compound (1).
To introduce substituent X in to the benzene ring, a raw material, in which X has been previously introduced can be used, or, X can be easily introduced by a well-known reaction at any step. Embodied examples are shown in the following. (In the following formulas, Rx shows the following group). 
wherein R, and Y1-Y4 show the same meaning as described above. 
wherein Y5 and Y6 have the same meaning as described above.
Namely, as shown in scheme 3, compound (5) and a lithium compound such as n-butyllithium and iodine are reacted to obtain compound (6). Compound (6) and sodim trifluoroacetate/copper iodine (I) (G. E. Carr et al., Journal of the Chemical Society Perkin Trans Actions I, 921 (1988)) or methyl fluorosulfonyldifluoro acetate/copper iodide (I) (Q. Y. Chen et al., Journal of the Chemical Society Chemical Communications, 705 (1989)) can be reacted to obtain trifluoromethyl compound (7).
As shown in scheme 4, compound (5), a lithium compound such as n-butyllithium, and a formylation agent such as N-formylpiperidine (G. A. Olah et al., Angewandte Chemie International Edition in English, 20, 878 (1981)), N-formylmorpholine (G. A. Olah et al., The Journal of Organic Chemistry, 49, 385 (1984)) or dimethylformamide (DMF) (G. Boss et al., Chemich Berichte, 1199 (1989)) can be reacted to obtain compound (8), and the reactant can be reached with a fluorinating agent such as diethylamino sulfur trifluoride (DAST) (W. J. Middleton et al., The Journal of Organic Chemistry, 40, 574 (1975), S. Rozen et al., Tetrahedron Letters, 41, 111 (1985), M. Hudlicky, Organic Reactions, 35, 513 (1988), P. A. Messina et al., Journal of Fluorine Chemistry, 42, 137 (1989)), or morpholino sulfur trifluoride (K. C. Mange et al., The Journal of Fluorine Chemistry, 43, 405 (1989) to obtain difluoromethyl compound (9).
As shown in scheme 5, after reducing compound (8) with a reducing agent such as sodium borohydride (SBH), lithium aluminum hydride (LAH), diisobutylaluminum hydride (DIBAL) or sodium bis(2-methoxyethoxy) aluminum (SBMEA) to obtain compound (10), the compound (10) can be reacted with a fluorinating agent such as DAST to produce monofluoromethyl compound (11).
As shown in scheme 6, compound (12) is changed to xanthate (13) by a method such as Albert et al. (Synthetic Communication, 19 547 (1989)). The resulting compound can be fluorinated by a method of Kurohoshi et al. (Tetrahedron Letters, 33, 29, 4173 (1992)) to produce trifluoromethoxy compound (14).
In addition, as shown in scheme 7, compound (12) is fluorinated is a system of chlorodifluoromethane/sodium hydroxide (Japanese Patent Laid-open 3-500413) to produce difluoromethoxy compound (15). Otherwise, it can be produced by a method of Chen et al. (The Journal of Fluorine Chemistry, 44, 433 (1989)).
The halogen compound and dihydroxyborane derivative, which are raw materials, can be produced by a well-known method of common organic synthesis, for example, a simple method as shown in the following. 
wherein R, X, Xa, Y1, Y2, Y5 and Y6 show the same meaning as described above.
Namely, as shown in scheme 8, by reacting compound (16) with a lithium compound such as n-BuLi and iodine or bromine, halogen compound (7) can be produced.
As shown in scheme 9, by the reaction a grignard reagent prepared from halogen compound (18) and magnesium, with a borane derivative such as trimethoxyborane or triisopropyloxyborane, and then by hydrolysis with hydrochloride or the like, dihydroxyborane derivative (19) can be produced.
The compound, not shown in the schemes, having xe2x80x94Oxe2x80x94 in group R of general formula (1) can be produced by reacting a halogen compound and alcohol or phenol in a solvent such as dimehylsulfoxide, DMF, 1,2-dimethoxyethane, tetrahydrofurane, hexamethylphosphric acid triamide or toluene in the presence of a base such as sodium amide (J. B. Right et al., Journal of the American Chemical Society, 70, 3098 (1948)), potassium carbonate (W. T. Olson et al., Journal of the American Chemical Society, 69, 2451 (1947)), triethylamine (R. L. Merker et al., The Journal of Organic Chemistry, 26, 5180 (1961)), sodium hydoxide (C. Wilkins, Synthesis, 156 (1973)), potassium hydroxide (J. Rebek et al., The Journal of Organic Chemistry, 44, 1485 (1979)), barium hydroxide (Kawabe et al., The Journal of Organic Chemistry, 37, 4210 (1972)) and sodium hydride (C. J. Stark, Tetrahedron Letters, 22, 2089 (1981), K. Takai et al. Tetrahedron Letters, 21, 1657 (1980)).
The above reactions are well-known, and if necessary, the other known reactions can also be used.
The liquid crystalline compounds of the present invention obtained thus have a very high voltage holding ratio, a low threshold voltage, very little variation of these properties with temperature and high xcex94n, and these compounds can be easily mixed with various liquid crystal materials and have good solubility at a low temperature.
In addition, the liquid crystalline compounds of the present invention are physically and chemically very stable under common conditions when the compounds are used for liquid crystal display devices, and are very excellent as a constituent of nematic liquid crystal compositions.
The compounds of the present invention can be preferably used as a constituent of liquid crystal compositions for TN, STN and TFT.
The liquid crystal compositions of the present invention preferably contain at least one compound represented by general formula (1) at a ratio of 0.1-99.9% by weight to develop excellent characteristic.
More particularly, the liquid crystal compositions provided by the present invention are finally obtained by mixing at least one compound represented by general formula (1) as a first component with the compounds selected from the group comprising of compounds represented by general formulae (2)-(9) according to the purpose of the liquid crystal composition.
As preferably embodied compounds represented by general formulae (2)-(4) are used in the liquid crystal compositions of the present invention, the following compounds are exemplified. 
wherein R1 and X1 have the same meaning as described above.
The compounds represented by general formula (2)-(4) have positive dielectric anisotropy values, excellent thermal and chemical stability, and are especially useful for preparing liquid crystal compositions for TFT which require high reliability, i.e. high voltage holding ratio and high specific resistance.
For the preparation of liquid crystal compositions for TFT, the quantities of the compounds represented by general formula (2)-(4) may be within the range of 0.1 to 99.9% by weight, preferably 10 to 97% by weight, and more preferably 40 to 95% by weight relative to the total weight of the liquid crystal composition. The compounds represented by general formula (7)-(9) may further be combined for adjustment of viscosity.
The compounds represented by general formula (2)-(4) may also be used for the preparation of liquid crystal compositions for STN and TN. The quantities of the compounds are preferably 50% by weight or less.
As the compounds represented by general formula (5) or (6), the following compounds are preferably used. 
wherein R2, R3 and X2 have the same meaning as shown in the above.
The compounds represented by general formula (5) or (6) have high positive dielectric anisotropy values, and are used especially for lowering the threshold voltage of the liquid crystal composition. The compounds are also used for adjusting optical anisotropy values and expanding the nematic range through, for example, raising clearing points. Further, the compounds are used to prepare liquid crystal compositions for STN and TN to improve the steepness of their voltage-transmittance correlation curve.
The compounds represented by general formula (5) or (6) are especially useful for preparing liquid crystal compositions for STN and TN.
When the quantity of the compounds represented by general formula (5) or (6) is increased, the threshold voltage of the liquid crystal compositions is lowered and the viscosity of increased. Accordingly, so long as the viscosity of the liquid crystal composition satisfies requirements, use of such compounds in large quantities is advantageous for low-voltage operation. The quantity of the compounds represented by general formula (5) or (6), in case of preparation of liquid crystal compositions for STN or TN, may be within the range of 0.1 to 99.9% by weight, preferably 10-97% by weight, and more preferably 40-95% by weight.
Preferred compounds represented by general formulae (7)-(9) may be exemplified below. 
wherein R4 and R5 have the same meaning as described above.
The compounds represented by general formulae (7)-(9) have small absolute values of dielectric anisotropy, and these are nearly neutral. The compounds represented by general formula (7) are mainly used for adjusting viscosity and optical anisotropy values. The compounds represented by general formula (8) or (9) are mainly used for expanding the nematic range through, for example, raising clearing points or adjusting optical anisotropy values.
Increase in the quantity of the compounds represented by general formulae (7)-(9) increases the threshold voltage and lowers the viscosity of the liquid crystal composition. Therefore, so long as the threshold voltage of the liquid crystal composition satisfies requirements, use of the compounds in large quantities is preferred. The quantity of the compounds represented by general formulae (7)-(9), in case of preparation of liquid crystal compositions for TFT, may be preferably 40% by weight or less, more preferably 35% by weight or less. In case of preparation of liquid crystal compositions for STN and TN, it may be preferably 70% by weight or less, and more preferably 60% by weight or less.
Moreover, in the present invention, except in special cases such as liquid crystal compositions for an OCB (Optically Compensated Birefringence) mode, an optically active compound is normally added to the liquid crystal composition of the present invention for adjusting the required twist angle by inducing formation of the helical structure of the liquid crystal composition, and for preventing reverse twist. Although any known optically active compounds may be used in the present invention for the above purposes, as preferred compounds, the following optically active compounds may be exemplified. 
In the liquid crystal compositions of the present invention, the pitch of twist is adjusted by addition of these optically active compounds. The pitch of twist if preferably adjusted within the range of 40-200 xcexcm for liquid crystal compositions for TFT and TN, and 6-20 xcexcm for liquid crystal compositions for STN. In case of a bistable TN mode, it is preferably adjusted within the range of 1.5-4 xcexcm. For adjustment of the temperature dependence of the pitch, two or more optically active compounds may be added.
The liquid crystal compositions of the present invention are prepared by well known methods. In general, a method in which various compounds are dissolved in each other at high temperature is used.
Furthermore, the liquid crystal compositions of the present invention may be used as those for the guest-host (GH) mode by adding dichroic dyes such as melocyanin, styryl, azo, azomethyne, azoxy, quinophthalon, anthraquinone and tetrazine types. Moreover, the compositions may be used for NCAP, which is prepared by micro-capsulation of a nematic liquid crystal, or for a polymer dispersion liquid crystal device (PDLCD) represented by a polymer network liquid crystal device (PNLCD), which a polymer of tridimensional network structure is prepared in liquid crystal. In addition, the liquid crystal compositions may be used for an electrically controlled birefringence (ECB) mode or a dynamic scattering (DS) mode.
The following liquid crystal compositions containing the compounds of the present invention can be exemplified. Moreover, the compounds in the composition examples and undermentioned working examples are represented by brief symbols in accordance with the rules expressed in the following tables, and the numbers of the compounds are the same as those in the following examples. Further, in the composition examples and working examples, except where noted otherwise, xe2x80x9c%xe2x80x9d means xe2x80x9c% by weight.xe2x80x9d
The following examples illustrate the present invention more specifically. In each example, C is a crystal, SA is a smectic A phase, SB is a smectic B phase, SX is a smectic phase wherein the phase constitution remains to be analyzed, N is a nematic phase, Iso is an isotropic phase, and the unit of phase transition temperature is xc2x0 C.